Increasing the Range of a Wireless BBQ Thermometer (rev 2)

About: I love combining software, electrical, and mechanical engineering to come up with unique and fun projects. I'm not a chef, but love to cook. Follow me on http://manganlabs.com and http://twitter.com/@mangan...
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This Instructable will describe a very simple process for increasing the range of a wireless BBQ thermometer.

While the process should be similar for almost all RF thermometers, the specific model I'm hacking is a "Maverick RediChek Remote Wireless Smoker Thermometer Model ET-73". It can be purchased from my Amazon store here: http://astore.amazon.com/johspro-20/detail/B0000DIU49

This is functionally a fantastic remote thermometer. It has two temperature probes (one for food, one for smoker) with completely independent alarm settings. It's consistent downfall (as you may find from numerous user reviews) is range. Maverick claims 100' which I have verified to be true providing both the transmitter and receiver are outside and in line-of-sight of each other. As soon as you step in the house (or even behind a tree when far away) the signal is either blocked or range is drastically reduced. Other than that, most people seem to like it. This hack solves that problem.

Hopefully this will help some of you out. From start to finish this took me about 30 minutes. I would expect it to take 1 - 2 hrs if you're not familiar with the parts or basic electronics hacking.

Note: For those of you already familiar with "rev 1" of this Instructable, "rev 2" adds the following:

Found and implemented ideal antenna length - 6.7" (based on whitepaper found here)

Step 1: Gather Materials and Tools

1.) Materialsa.) 6.7" of 22 gauge copper or steel wire
The antenna will require 6.7" of 22 gauge copper or steel wire which is commonly found at craft stores and used for flower arrangements. 22 gauge is perfect because it will bend and stay in place. You can coil it up for storage and point it out straight when in use.

Why such an exact length? Because antenna length is directly tied to the operating frequency (433.92Mhz) in which the device was designed for. There is a specific formula used to calculate the length which is what I used to derive 6.7". You still may get improved performance with a longer or even shorter antenna, but it won't be maximum efficiency.

Ideally the wire should be non-coated. If it is coated (as mine was) you will just have to sand the paint off one end for soldering.

b.) One Antenna Tube
In addition to making the project look very professional, the antenna tube protects your wire from breaking off, reduces strain on the PCB, and helps keeps water out (of the antenna hole). While any standard hobby antenna tube can be used, this Instructable is based on one from Dubro Racing, Model 2338 (Red, with cap). It can be seen and ordered here: http://astore.amazon.com/johspro-20/detail/B000BP4JC4

Finally, it is assumed that you already have a thermometer that you are willing to hack (which has obvious risks such as breaking the device if you're not careful). If you want to purchase a thermometer I highly recommend the same one I used (Maverick RediChk Model ET-73) here: http://astore.amazon.com/johspro-20/detail/B0000DIU49

Step 2: Remove Back of Transmitter

WARNING!!!! - Proceed at your own risk! There is always a possibility that you might break your thermometer. This will also void your warranty!

First of all, make sure you are working with the transmitter and not the receiver (see photos below for transmitter).

Remove the 6 screws on the back of the transmitter. You may not be able to take them out completely due to rubber washers on the inside of the case. Be careful not to lose the screws or rubber washers.

Step 3: Remove PCB

After the screws are loose, carefully separate the case. You will not have much room to work because of wires connecting the two halves.

Caution: The LCD display is held on by nothing other then pressure from the circuit board. It will fall out very easily after you remove the PCB so be careful not to drop it.

The case halves can now be safely pulled apart and the PCB removed (again, be careful you don't drop that LCD when pulling apart. It will break very easily).

Note: You could skip this step if you feel that you have enough working room with the PCB mounted in the case. I personally wanted to remove it from the case so I could easily sand and solder it. If you want to sand and solder while in the case then skip this step.

Step 4: Find the Antenna

Let me digress for a moment...
Sometimes you search the internet for information about a product with very little luck. This was the case for for me. Nothing was available other than the product manual. When this happens it's worth while to search on the FCC ID of the product. Doing so may result in much greater detail about the product as it was filed with the FCC (circuit diagrams, block diagrams, internal photos, test reports, etc.). This is all public information but not typically indexed by search engines.

In this case it's pretty clear just by looking at it but sometimes they are not this obvious. Either way it's always good to be absolutely sure before you start hacking away at it!

Note that I have another Instructable on this topic HERE (created for a contest in which I lost but was one of the finalists!)

Step 5: Modify Antenna

Now it's time to extend your antenna.

1.) Cut a piece of your 22awg wire to exactly 6.7". Through a bit of research I've determined that this is the ideal size for this thermometer which operates at 433mhz and a 1/4 wave length antenna (feel free to ask if you want more technical detail on this).

2.) Using your file or sandpaper, rough up about 1/4" of wire at one end. Don't skip this step even if you already have bare wire. It helps to remove oxidation which will make soldering easier.

3.) Using your file or sandpaper, carefully remove about 1/4" of the green coating from an area of the PCB antenna. Sand just enough so the copper becomes exposed but be very careful not to sand the copper right off.

The location you sand doesn't need to be exact but should be very close to what I have below so everything lines up correctly later. The wire will need to exit the case at a right angle from the PCB with minimal bends as further described below.

4.) Now it is time to solder the wire to the PCB as shown below. The antenna wire should leave the circuit board at 90 degrees like this __|__ (I straightened mine below as I was putting the housing back together). If you put a bend in the wire it may add impedance which can result in a drop in signal gain.

I assume you already know how to solder. Using flux helps in this case but it is not required. Just make sure you end up with a nice solid connection.

Step 6: Drill Hole and Thread Antenna

Almost done!

Now drill a 1/8" hole in the top of the case where the antenna will protrude out. Set the PCB in place where it is going to be (when reassembled) and eyeball where the hole needs to go. It doesn't need to be perfect but should be close to allow a 90 degree exit from the board and minimize the bending required for adjustment.

7.) CAREFULLY close the case, adjusting antenna wire as you are closing. Take your time with this step!

8.) Tighten all 6 screws on the back of case and we're ready to test!

Step 8: Testing

Now conduct a quick test to make sure you didn't break anything. With no probes attached you should see three dashes on the LCD. This confirms the LCD is correctly seated and you didn't break any of the power wires.

You should continue to conduct a full test with both probes to confirm connectivity on their internal wires.

If all is well, proceed with the next step...

Step 9: Attach Antenna Tube

While one could argue that the antenna tube isn't necessary, I really think it is after going through one revision of this project without it.

Without the tube the wire is VERY easy to bend excessively. This weakens the solder joint and adds stress to the PCB which currently has no real strain relief. The tube also makes the project look very professional, as if you bought it this way!.

Stop! Don't continue with this step until you have confirmed that the thermometer is working (as noted in step 8). It will save you a ton of aggravation if you have to disassemble the unit again.

Final Assembly Steps:

First make sure the antenna wire is as straight as possible. Gently bend to adjust if necessary.

Remove antenna tube from package. You won't need the very small rubber piece that is used to secure small wire antennas with RC cars. You should have just the tube and cap.

Cut the tube down to 7" in length

Apply super glue to the antenna hole and last 1/4" of antenna tube as shown in the two photos below.

With the glue side down, slide antenna tube down antenna. Push into hole. It should go in about 1/4".

Apply small amount of super glue to outside top of antenna. Also apply a small drop to the inside of the antenna tube cap.

Slide on the tube cap.

Allow glue sufficient time to dry and you're done! (see next step for results)

Step 10: Final Results

Yeah! Were done!

If all goes well you just increased the range of your thermometer by at least 3 - 4 times. It now easily goes through walls (within reason) and you should receive a much stronger signal while in your house (pretty much anywhere). I walked around my entire house without loosing signal at all.

I hope you have enjoyed my first Instructable! Feedback for improvement is very much welcome. More to come in the near future!

Step 11: Additional Info / Possible Enhancements

If this was helpful, please rate my Instructable!

Also subscribe if you want to stay posted on my future instructables as they are created!

I would love to hear from any armature, pro or semi-pro BBQers that have used this hack with success!

Thanks in advance for your vote!

- John

Side Notes / Possible Enhancements
a.) It is also possible to modify the antenna on the receiver side for potentially even greater range. I personally didn't find that this was necessary. I'm getting fantastic range with just the transmitter modified.

Most mods for this particular thermometer I have seen to date are on the receiver rather than the transmitter. For me it made more sense to amplify the signal going out rather than increase the "listening" side for an already weak signal. Modify both sides and you'll probably get even better results but I honestly don't see any need for this unless you want to monitor your temps from VERY far way.

b.) Taking this a step further, you could also make the antenna detachable for easy storage.

c.) One other complaint about this thermometer is the location of the on/off switch inside the transmitter. You need to remove the battery back to turn it on or off. They do this to make it water resistant. You could easily relocate a switch to the outside of the case where it is more convenient. (I cover my thermometers when it starts to rain anyway - another good reason for this external antenna!). Here is one mod I found to ease access to the switch: http://www.youtube.com/watch?v=tBk5rUGQ4xU (thanks to the author for also linking back to my Instructable!)

Other Tips For Use

Regardless of thermometer make/model, you should foil your probes! Wrap a very thick piece of foil about 4 - 5" long over the joint where your probe wire meets the metal probe tube. It should be several wraps and will be quite bulky (and ugly) when done. This area is the weakest part of the probe and it is very common for people to melt the probe with high temperature (and blame it on the thermometer manufacturer). I've melted probes myself in the past but have never lost a probe since I started using this technique.

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24 Discussions

Thanks so much for this instructable. It worked like a charm (and I had enough room so I didn't have to remove the PCB). I tested the improvement by putting the probe in water that I was heating up and walked past my neighbor's house and was still getting a reading!!!!

Thank You so much I can now read bbq temps throughout my home before had to leave the receiver in kitchen close to back patio where my acorn grill was. Saved me from having to shell out some cash for more powerful unit. Thanks again works awesome

Thanks for this information! I applied it, although in a slightly different way, to extend range of my Acurite wireless house thermometer. The Acurite, however, uses a helical spring antenna. I may do an instructable on it at some point if there is enough interest.

Thanks for this instructable. After completing the xmit mod my range did improve about 2X. So I decided to do the receiver mod also. Both mods work and do improve the range but I do wish for still more. My house has Hardy cement siding, I think that really is a block to this device. With both mods, 50 ft and a couple of walls still makes it iffy.

I tried this mod, but was really bummed when it didn't work for me. I did it EXACTLY how it's posted here, checked it 3 times, and I know I didn't make any mistakes. In fact, after I finished, my range was just as it always had been and nothing better - about 3 feet, which as you know, sucks.

So, having nothing to loose at this point, I tried modding the receiver with the SAME length of wire (17.018 cm) and....it works!!! It works like a charm!!!

Thanks for posting this. Now I can read my grill temp through a 3 course brick wall, two interior plaster walls, all about 35 ft away. I'm very happy!

By the way...forgot to mention. If you're having trouble and want to try modding the receiver too, open up the receiver, and you'll see a small circle of (about the size of a dime) on the PCB near the top of the board. THIS is the receiver antenna. I didn't scrape or sand anything down to solder the antenna wire. I simply soldered to the first component NEAREST the circle. (See image. Blue arrow is what I believe to be the receiver antenna. Red arrow is where I soldered my wire.)

This worked slick! Very informative and practical. Question- can you give a resource or formula for figuring out appropriate antenna length in relation to the mhz value in a given device? This would be useful info for other projects where I might want to extend the range. Thanks!!

Great Instructable! I would not have attempted this without your instruction. Alas it did not work for me so I am trying to figure where I went wrong. In my first attempt, my belief was that the antenna on the board was the metal layer under the green and I soldered to that, even though the metal was silver colored and not copper. Since that didn't work, I thought there may be a copper wire running under the silver. Not finding anything, I re-soldered my antenna and ran enough solder between the gap. In my two attempts, the distance readings still remain the same as if I had done nothing and an obstruction like the window of the sliding glass door hinders it greatly, and passing thru a wall is impossible. Is there some test I can do with a multi-tester to see if my antenna that I added is functioning ? Do you have any other comments where I might have messed up? Thanks for any help!

What I would like to have is a large display. Have you considered tapping into the leds to get large leds? I would like a display of about 2" numbers. I would like them to be mounted at right angles to each other such that they would be visible for 180degrees. Would this be feasible? I realize adittional power would be required. However, it would be nice to look from 60' away to see the oven temperature and the meat temperature.

That could definitely be done as an add-on or replacement to the existing LCD, but it would be a much more involved project. It would probably require the use of a microcontroller (like an Arduino) to hijack and re-interpret the LCD output to drive LEDs.

Thanks a lot for this instructable! It was very detailed and things went exactly as they should have. It really didn't take very long at all. Before the mod, mine had a range of about 15 feet (through one sliding glass door), after the mod I tested at least 100 feet through 3 or 4 walls.

Such a simple solution to such a common problem. The best thing about this is your advice on the FCC search -- I have all sorts of small wireless devices that the circuit diagram would be helpful for. Thanks!
Is there room to add a retractable antenna? Radio Shack sell replacement antennas for radios and remote control toy controllers.

Your the third person today to say they loved that piece about the FCC search! Glad I could help!
I thought about a retractable antenna but none of the ones I had in "stock" were small enough. It is pretty tight inside the case. You could probably find an antenna that could run along the outside or back of the case. I'm not sure if that would help or hinder the range though. Some antennas are designed to work at specific frequencies. This operates at 433MHz (again, info I extracted from the FCC search). That plain ole' piece of wire seems to work pretty good for this frequency but maybe I'll try something else in the future and compare the results.
I've also been told that you can "tune" to the ideal frequency by slowly cutting the wire down and testing after each cut. If I had better equipment (such as an oscilloscope) I could probably figure out the exact length that would be ideal for this device. Oh well, it works great for me now as-is!
Thanks for the feedback!
- John

silicanghost...Did the mod and it works, but I'd really like to find a retractable antenna. Have you had any luck with that? It can even be one that sits on the outside of the unit. Thanks for the mod. Derek

A retractable antenna would be nice. That was actually in my original plans for the mod (I still have the antennas which I bought from Radio Shack). After I researched it a bit, I learned that the antenna length should be matched with the frequency of the crystal for best performance (and in some cases, for it to work at all). Most people said to just try a wire which is what I did. It worked so well that I didn't bother looking into the retractable antenna again.

The overall length of the antenna from the top of the case out should as close to 6.7" as possible (as per my calculations anyway). Try finding a retractable antenna that meets those specs and see how it works. Note that your jumper between the circuit board and the antenna needs to be very straight, and cleanly soldered. Bends and spikes in a cold solder joint can affect the overall impedance and as a result, the overall performance.